Method of manufacturing an electric incandescent lamp having a longer lifetime and/or a higher light output

ABSTRACT

The invention relates to a method of manufacturing a gas-filled electric incandescent lamp particularly a low-voltage incandescent lamp in which the wire diameter of the incandescent civil varies in different axial sections. The diameter of the tungsten wire is reduced at the end turns and is increased in the middle with the aid of a chemical cycle process either before or after mounting in the lamp in order to reduce the temperature differences between the turns in the middle and at the end of the coil during operation of the lamp at the prescribed operating voltage.

United States Patent Kauer et al.

111 3,868,159 14 1 Feb. 25,1975

OTHER PUBLICATIONS J. Schroder, Examples from fluorine chemistryand possible industrial applications," Philips Technical Review, Vol. 26, No. 41516, 1965, pp. 111-116.

[ Inventors: Erhard Kauer; J gsghm l-l. Horster et al., The burn-out mechanism of incanboth of Aachen; Horst descent lamps, Philips Tech. Rev. 32, No. 6/7/8, Roetgen, all of Germany 6/16/72, pp. 155-164.

[73] Assignee: U.S. Philips Corporation, New

YOrkN'y Primary Exammer-..Roy Lake Assistant Examiner.lames W. Davie [22] Ffled: June 1973 Attorney, Agent, or FirmFrank R. Trifari [21] Appl. No.: 369,552

- [57] ABSTRACT {301' Foreign Application Priorit D t The invention relates to a method of manufacturing a June 28, 1972 Germany 2231520 gas'fined eleftric lamp, palticulifly a low-voltage mcandescent lamp 1n which the w1re di- [52] us CL 316/1 29/25 17 I ameter of the incandescent civil varies in different [51] Im h M axial sections. The diameter of the tungsten wire is re- [58] Fie'ld 17 18 19 duced at the end turns and is increased in the middle 5 5 with the aid of a chemical cycle process either before l or after mounting in the lamp in order to reduce the differences between the turns in the mid- [56] References Clted temperature dle and at the end of the cod durmg operatlon of the UNITED STATES PATENTS lamp at the prescribed operating voltage. 3,619,701 ll/l97l Sugano 313/222 3,759.602 9/1973 Walter 316/20 7 Claims, 3 Drawing Figures wmrwwwm a r A Q j j V 1 IL! 1 A f [fl/7] r \"\\\;XI

.A I I: i

METHOD OF MANUFACTURING AN ELECTRIC INCANDESCENT LAMP HAVING A LONGER LIFETIME AND/OR A HIGHER LIGHT OUTPUT Low-voltage lamps are in this connection to be understood especially heavy-loaded electric incandescent lamps whose operating voltage is generally below 42 V. Examples of such lamps are many types of projection lamps, motorcar lamps, etc. in which a high luminance is important. The lamps may comprise a reactive transport gas such as iodine and bromine and bromine compounds such as hydrocarbonbromides, hydrobromic acid, boronbromide, etc. These lamps generally have a coiled filament which consists of a comparatively low number of turns. By removal of heat through the ends of the coiled filament the temperature of the end turns may be several hundred C lower than the temperature of the turns in the middle of the coiled filament. Consequently the luminance along the coiled filament is not It hasbeen found that in case ofa reduction of the"? 'takes place during operation in addition to the already constant for which reason in projection lamps sometimes only the light emitted by the central turns is used in order to obtain an optimum uniform light intensity on the image surface. It has already been attempted to equalize the luminance distribution along the coiled filament by pre-operation in a halogen-containing gas at- 'mosphere. It was always the aim in such methods of pretreatment to reach a full temperature homogeneization along the filament.

However, in practice, such pre-operation treatments did not find general acceptance. This is caused presumably by the fact that such pre-treatments ledto considerably shorter lifetimes.

An object of the invention is to provide a method of manufacturing an electric incandescent lamp, particularly a low-voltage incandescent lamp having a longer lifetime and/or a higher luminance which is as uniform as possible. According to the invention this goal is achieved by a method in which the filament is preoperated until the temperature T of the end turns of 40 the filament is 20 to l20K lower than the temperature T of the central turn in an atmosphere which comprises a gas which is reactive relative to tun gsten.

The invention is based on the following recognitions obtained during experiments which led to the present invention. In the conventional low-voltage lamps the temperature of the end turns is often 200 to 400K lower than the temperature in the middle of th e fil ament. Such a coiled filament will burn through in the central hotter part of the filament. When the temperature along the filament body is completely equalized; the filament burns through at one of the ends. An extension of the lifetime does not occur, on the contrary the lifetime is generally drastically shortened. Hitherto it has not been taken into account that at equal temper- 60 mentioned radial tungsten transport. In case of temperature differences of approximately 5K between two juxtaposed turns this transport form turn to turn is already larger than the radial transport at a filament temperature of approxiimately 3000K bringing about the loss of mass of the filament body. In filaments having comparatively short and thick wires such as are used in high-loaded low-voltage incandescent lamps the temperature from turn to turn decreases, however, by more than 5K as a result of the strong heat dissipation through the supply conductors. By complete equalisation of the temperature of the coiled filament, this axial transport would not occur, but in such a case the radial transport from the end turns as described would result in a considerably shorter lifetime. It has been found that for the required temperature decrease in the direction of the two end turns of from 20 to l20K particularly between 30 and K, the radial tungsten losses of the end turns correspond to the total loss of the turn in the middle of the filament body, which loss is composed of radial and axial transport, so that in addition to a more uniform luminance at a constant temperature T of the middle of the filament an increase in the light output and an extension of the lifetime r are obtained. Furthermore it has been found that the largest extension of the lifetime is obtained when the mass losses of each individual turn between the middle and the ends of the filament likewise equals the loss of the central turn and hence that of the end turns because evidently the unfavourable formation of local differences in cross-section and in temperature (so-called hotspots") is counteracted thereby. Such mass losses which are uniform for all turns are achieved in the ideal case when the temperature variation T(x) along the filament axis x from the middle of the filament X O and the temperature T5 to the ends of the filaments x L and the temperature T, satisfies the following equation:

exa-1+xa 1/3, elal+la 'has a value of between 38 and 29 and in the temperature range about 3,300K which is conventional for |ow-voltage lamps may be adjusted at 32. In the formula a corresponds to the radius of the quasi-stationary layer of gas (Langmuir-layer) surrounding the filament.

- In the above-mentioned temperature range of between approximately 2,800K and 3,600K this radius may assame a value of between 1 and 4 mm. For the temperature range about 3,300K the radius is approximately 2 mm.

The incandescent lamp according to the invention may be manufactured by pre-operating the lamp with th mealtime"; lzerlxeakxee:aesr tinsfie ile ment body prior to mounting, the filament body being in an atmosphere comprising fluorine or chlorine.

Fluorine is preferred. Only when using fluorine is it possible to preoperate the filament body at a tempera ture which can also be achieved later during operation at the operating voltage which has been found to be favourable in the experiments for adjusting a given temperature profile and hence a long lifetime. With fluorine at temperatures of the filament body of about 3,300K which are conventionally usedin the present-' day high-loaded low-voltage incandescent lamps tungsten is transported from comparatively cold spots to hotter spots of the filament body. With chlorine this is only the case at temperatures of less than approximately 2,700l(. In addition the pretreatment with fluorine has technological advantages relative to a pretreatment with chlorine. When using chlorine all parts of the equipment coming in contact with the reaction gas must be maintained at a temperature of at least 200C because at low temperatures the less volatile tungsten chlorides condense and hence are withdrawn from the reaction or may give rise to clogging of the gas ducts. When using fluorine these difficulties do not occur because all reaction products occurring in the treatment with fluorine are gaseous at room temperature. In addition the transport process in the presence of fluorine is considerably faster than in the presence of chlorine, Furthermore it has been found that already during a short pre-operation of only a few minutes in a fluorinecontaining atmosphere the surface of the filament is.

uble homogenization can be observed. By suitably The partial pressure of the inert gas is preferably between approximately- 0.1 and 10 atmospheres. The pre operating temperature must be approximately between 2,800 and 3,600K. Under these circumstances the pre-operation time is approximately 1 minute to 20 minutes.

When pre-operating in a chlorine-containing atmosphere such a quantity of a volatile chlorine compound is preferably added to the gas atmosphere that in case of complete decomposition the partial pressure at room temperature of chlorine would be between 10 and 100 Torr. When using chlorine in an elemtary form the partial pressure is likewise chosen to be between these limits. The partial pressure of theinert gas is preferably be-.

tween'approximately 0.l and I atmospheres. The pre operation temperature must be approximately between 1,700 and 2,7OQK. Under these circumstances the.

pre-operation period is approximately to 100 minutes.

The lamps with a filament treated according to the invention may be filled with the conventional rare gases such as argon or krypton or may also comprise a chemical transport gas such as iodine or bromine or bromine FIG. 1 diagrammatically shows in a cross-section a pre-operation device 7 FIG. 2 shows a complete lamp having a preoperated filament and choosing the partial pressures of fluorine and inert gas r of which are more easy to handle than fluorine, are, for

example, tungsten hexafluoride (WF tungsten oxyfluoride (WOF nitrogen fluorides (NF N F fluorides of phosphorus and arsenic, sulphur hexafluoride.

(SP oxygen fluoride (0P selenium hexafluoride (SeF tellerium hexafluoride (TeF ),haIogen fluorides, fluorides of rare gases such as, for example, xenon fluorides.

The partial pressure of these compounds is prefera bly chosen to be such that in case ofa complete decomposition of the compound the partial pressure of fluorine at room temperature should be between approximately 0.] and Torr. Also when using fluorine the partial pressure is preferably chosen to be within these limits. In case of partial pressures of less than (H Torr thc required pro-operation time considerably increases and in case of partial pressures of more than 20 Torr the reactions proceed too vigorously and the process becomes uncontrollable.

. EXAMPLE Tungsten filaments 1 were pre-operated in a preoperation device diagrammatically shown in a crosssection in FIG. 1. The device contained two nickel electrodes 3 provided with nickel tubes 2 which were secured toa base plate 4 of electrically non-conducting material, in which electrodes the filament ends 6were inserted. The gasspace was enclosed within an envelope 5 of nickel.

The filaments 1 had 18 turns. The wire thicknesswas 0.17 mm and the filament length was 5 mm.'The straight wire ends 6 were protected from quick attack by fluorine over a length of approximately 5 mmby the nickel tubes 2 (inner diameter 2 mm). The envelope 5 comprised a gas mixture of argon (partiallpressure 200 I Torr) and nitrogen fluoride (NF (partialpressure3 shown in FIG. 2, provided in a quartz envelope. The

The curves A and B in FIG. 3 show temperature profiles (pertaining to one half of a filament each) of nontreated filaments. The curves C and D show temperature profiles of filaments treated in accordance with the invention (also pertaining to one half of a filament). The temperature profiles C and D satisfy the temperature requirements very good while the non pre-treated temperature profiles show a temperature profile deviating therefrom. In the Figure the reference Nr W shows the number of the relevant turn, A T(K) shows the temperature difference in K and M shows the middle of the filament.

The resultant lighttechnical advantages of the lamps A C and D having pre-treated filaments with respect to those having non pre-treated filaments A and B are apparent from the Table below in which the measured light values and the lifetimes of the four experimental lamps are stated. All lamps were examined at the same operating temperature T,,, (temperature of the middle of the filament). The electrical power N, the luminous flux I, the light output l/N, the temperature difference A T between the middle and the ends of the filament and the lifetime 7 until the wire burnt through were measured. The measuring results are representative of The advantages obtained by the invention thus especially consist in that with the aid of comparatively simple steps an extension of the lifetime and a higher and more uniform luminance of gas-filled incandescent lamps can be obtained.

What is claimed is:

l. A method of manufacturing a gas-filled electric incandescent lamp, particularly a low-voltage incandescent lamp in which the wire diameter of the filament body consisting of a coiled tungsten wire varies in different axial sections of said coil, said diameter being reduced at the end turns and increased in the middle with the aid of a chemical cycle process either before or after mounting in the lamp so as to reduce the temperature differences between the turns in the middle and at the end of the filament during operation of the lamp at the prescribed operating voltage, said method comprises mounting said filament and in an atmosphere comprising a gas which is reactive with respect to tung- 6 sten and pre-operating said filament until the temperature T of the end turns of the filament is 20 to 120K lower than the temperature T of the central turns.

2. A method as claimed in claim 1, wherein said preoperating step is continued until the temperature T, of

the end turns of the filament is 30 to K lower than the temperature T of the central turns.

3. A method as claimed in claim 1, wherein said preoperating step is performed in an atmosphere containing a chemical selected from the group consisting of fluorine in an elementary form, chlorine in an elementary form, a fluorine compound, and a chlorine compound.

4. A method as claimed in claim l, wherein said preoperating step takes approximately 1 to 20 minutes in an atmosphere comprising fluorine having a partial i pressure of between 0.1 and 20 Torr and an inert gas having a partial pressure of between 10 and 10 Torr at a temperature T of the central turns of between 2,800 and 3,600K.

5. A method as claimed in claim 1, wherein said preoperating step lasts 10 to minutes in an atmosphere comprising chlorine having a partial pressure of between 10 and 100 Torr and an inert gas having a partial pressure of between 10 and 10 Torr at a temperature T of the central turns of between l,700K and 2,700K.

6. A method as claimed in claim 1, wherein said preoperating step is performed in a fluorine-containing atmosphere until the temperature variation of the middle of the filament [(X =0, T to the ends [(X) L, T is within a temperature range which is limited by two curves given by the equation below:

exa-1+xa 1/(Y ela-14-l/a the other boundary curve.

O mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION patent 3,868,159 Dated February 25, 1975 ITWEHWTB) Erhard Kauer. Johann Schroder T-Trw i- T-To'ls't'e'r It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Title page, Section 30 change "2231520" to Claim 6, line 50 Change "2/(T to 2/= 1 Signed and Sealed this twenty-ninth D3) Of Jab 1975 [SEAL] AIIESIJ RUTH C. MASON Arresting Officer C. MARSHALL DANN (mnmixsiuner vflaunts and Trademarks 

1. A METHOD OF MANUFACTURING A GAS-FILLED ELECTRIC INCANDESCENT LAMP, PARTICULARLY A LOW-VOLTAGE INCANDESCENT LAMP IN WHICH THE WIRE DIAMETER OF THE FILAMENT BODY CONSISTING OF A COILED TUNGSTEN WIRE VARIES IN DIFFERENT AXIAL SECTIONS OF SAID COIL, SAID DIAMETER BEING REDUCED AT THE END TURNS AND INCREASED IN THE MIDDLE WITH THE AID OF A CHEMICAL CYCLE PROCESS EITHER BEFORE OR AFTER MOUNTING IN THE LAMPS SO AS TO REDUCE THE TEMPERATURE DIFFERENCES BETWEEN THE TURNS IN THE MIDDLE AND AT THE END OF THE FILAMENT DURING OPERATION OF THE LAMP AT THE PRESCRIBED OPERATING VOLTAGE, SAID METHOD COMPRISES MOUNTING SAID FILAMENT AND IN AN ATMOSPHERE COMPRISING A GAS WHICH IS REACTIVE WITH RESPECT TO TUNGSTEN AND PRE-OPERATING SAID FILAMENT UNTIL THE TEMPERATURE T1 OF THE END TURNS OF THE FILAMENT IS 20 TO 120*K LOWER THAN THE TEMPERATURE T2 OF THE CENTRAL TURNS.
 2. A method as claimed in claim 1, wherein said pre-operating step is continued until the temperature T1 of the end turns of the filament is 30* to 70*K lower than the temperature T2 of the central turns.
 3. A method as claimed in claim 1, wherein said pre-operating step is performed in an atmosphere containing a chemical selected from the group consisting of fluorine in an elementary form, chlorine in an elementary form, a fluorine compound, and a chlorine compound.
 4. A method as claimed in claim 1, wherein said pre-operating step takes approximately 1 to 20 minutes in an atmosphere comprising fluorine having a partial pressure of between 0.1 and 20 Torr and an inert gas having a partial pressure of between 10 and 104 Torr at a temperature T2 of the central turns of between 2,800* and 3,600*K.
 5. A method as claimed in claim 1, wherein said pre-operating step lasts 10 to 100 minutes in an atmosphere comprising chlorine having a partial pressure of between 10 and 100 Torr and an inert gas having a partial pressure of between 10 and 104 Torr at a temperature T2 of the central turns of between 1,700*K and 2, 700*K.
 6. A method as claimed in claim 1, wherein said pre-operating step is performed in a fluorine-containing atmosphere until the temperature variation of the middle of the filament ((X O, T2)) to the ends ((X) L, T1) is within a temperature range which is limited by two curves given by the equation below:
 7. A method as claimed in claim 6, wherein T2 - T1 30*K for one boundary curve and T2 - T1 70*K for the other boundary curve. 